In the medical field, reduction in wastes of processing solutions has been desired in recent years from the viewpoints of safeguarding the environment and saving space. Attainment of this desire requires new technologies regarding light-sensitive heat-developable photographic materials used for medical diagnostic purposes and photographic technology applications, which can undergo exposure with efficiency by use of a laser image setter or a laser imager and form clear black images having high resolution and high sharpness. It is possible for those light-sensitive heat-developable photographic materials to eliminate the necessity for using solutions of processing chemicals and to provide simple and environmentally friendly heat-developable processing systems for customers.
As fine depiction is essential to them, images for medical-care use are required to have high quality including high sharpness and excellent graininess, though such a requirement is also present in the field of general image-forming materials, and besides, they have a feature that it is desirable for them to have a cold black tone from a viewpoint of ease of diagnosis. At present, various kinds of hard copy systems utilizing pigments or dyes, such as inkjet printers and electrophotography, are distributed as general image-forming systems, but they are not satisfactory as output system of images for medical-care use.
On the other hand, heat image formation systems utilizing organic silver salts are described, e.g., in U.S. Pat. Nos. 3,152,904 and 3,457,075, and Thermally Processed Silver Systems by Shely in “Imaging Processes and Materials”, Neblette's 8th Edition, compiled by Sturge, V. Walworth & A, Shepp, p. 2 (1996).
In particular, a heat-developable photosensitive material has a light-sensitive layer ordinarily containing a catalytic amount of photocatalyst (e.g., silver halide), a reducing agent, a reducible silver salt (e.g., an organic silver salt) and, if needed, a toning agent for controlling the tone of silver, dispersed in a binder matrix. After imagewise exposure, the heat-developable photosensitive material is heated at a high temperature (e.g., at least 80° C.) to cause a redox reaction between silver halide or a reducible silver salt (functioning as an oxidizing agent) and a reducing agent, thereby forming a black silver image. The redox reaction is accelerated by the catalytic action of a latent image formed from the silver halide by exposure. Accordingly, the black silver image is formed in the exposed area. Those heat-developable photosensitive materials are disclosed in many documents including U.S. Pat. No. 2,910,377 and JP-B-43-4924 (the term “JP-B” as used herein means an “examined Japanese patent publication”), and Fuji Medical Dry Imager FM-DP L is available as a medical-care image formation system utilizing a heat-developable photosensitive material.
A heat-image formation system utilizing an organic silver salt is produced by a method of using a solvent for coating, or a method of applying and drying a coating composition containing an aqueous dispersion of polymer particles as a main binder. The latter method eliminates a step of recovering a solvent, so it permits simplification of production facilities and has an advantage in its suitability for mass production.
Since it has no fixation step, such an image formation system utilizing an organic silver salt has a serious problem with preservation after development processing, particularly deterioration of print-out under exposure to light. With the intention of improving the print-out phenomenon, the method of utilizing AgI formed by conversion of an organic silver salt is disclosed in U.S. Pat. No. 6,143,488 and European Patent No. 0922995. However, the method of converting an organic silver salt by the use of iodide as disclosed in those references cannot provide sufficient sensitivity, so it is difficult to form a practical system.
Other photosensitive materials utilizing AgI are described, e.g., in WO 97-48014, WO 97-48015, U.S. Pat. No. 6,165,705, JP-A-8-297345 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) and Japanese Patent No. 2,785,129. However, these photosensitive materials cannot achieve satisfactory sensitivity and fog level and fail to meet the practical use as photosensitive materials for laser exposure. Therefore, development of methods of successfully using silver halide having a high silver iodide content has been awaited.
On the other hand, the image formation method using blue to ultraviolet laser light and the sensitive material therefor are disclosed in JP-A-2000-305213, but Ag! is not used therein and the sensitivity thereof is insufficient.